Some of my fiddlings of the last 12 months with power cords are discussed in my PFO article on the Furutech Evolution II wiring suite. See:
http://positive-feedback.com/Issue45/furutech.htm
My general impressions is that there are power cords that are somewhat position insensitive, and can be successfully applied to most all positions in the component chain, like the Furutech Evo II featured in the review, which is my current general reference wire. Conversely, other power cords seem to be most applicable to a particular position or a particular component, e.g. the Shunyata Helix Anaconda Alpha, which I thought to be in highest synergy with the Esoteric X-01 CDp.Some other wires instead, I found not to be at all conducive to the sound I am seeking.
In the end, I suspect that the answer to the original question is. . . it depends! Depends on the individual component, on the overall architecture of the system, on the room acoustics, and on one's particular sonic/musical inclinations. G.